The Silhouette Script will allow you to change your RPC's to silhouettes including selecting their color and opacity for a more stylized look to your scene.
In order to run the script - download it from the web site and place it in the Script Directory with in Max/Viz. Once you have opened Max you can access the script through the Utilities Panel by selecting Max Script. From the Max Script rollout select Run Script and then rpc_silhouetter.ms. To now activate the script - select it from the Utilities drop-down menu. The RPC3 Silhouetter interface will now appear.
View the Tutorial here